The present invention relates to electrical power control circuitry and, more particularly, to an improved system for monitoring and correcting the power factor of a power installation which employs a power measurement integrated circuit.
Electrical power is an enormously versatile and convenient source of energy. However, there are costs in generating and distributing electrical energy, which tend to increase when demand for electrical power increases. For this reason, there is always a motivation for increasing the efficiency of electrical power transmission and utilization and, conversely, for reducing losses and wastes in the delivery and use of electrical energy.
Alternating current electrical power is characterized by a phase relationship between the current and voltage. Current phase lagging the voltage phase results from a preponderance of inductive loads, while current phase leading the voltage phase results from capacitive loads. An in-phase relationship results from resistive loads or a balance of inductive and capacitive loads. In-phase current results in “real” or resistive power, also known as active power, while out-of-phase current results in reactive power from the influence of inductive or capacitive reactance in the power circuit. The vector sum of active power and reactive power is called apparent power. In a single phase AC system, the angle between the active power and the apparent power is the same as the phase angle between the voltage and current. A commonly used measure of the phase relationship between current and voltage is power factor, which is equal to the cosine of the phase angle therebetween or between the active power and the apparent power. Power factor maximizes at a value of unity when the relationship is effectively resistive, is positive and less than one when inductive, and is negative and less than one when capacitive.
In practice, there tend to be more types of inductive loads, such as electric motors, transformers, and the like, connected to power lines than capacitive. In residential power installations, the majority of electrical energy consumed is in refrigeration, ventilation, air conditioning, lighting, and, in some cases, heating. Relatively small amounts of energy are also used for communications, computers, entertainment devices, and the like. Although reactive power is not “consumed” as such in useful work, it is delivered to the power system and returned to the generator. For this reason, there are energy losses associated with the delivery of reactive power, from resistive losses and from currents that are inductively and capacitively coupled away from power conductors. Thus, the delivery of reactive power affects the cost of power generation. Power companies often impose surcharges on industrial power customers when their loads drive the power factor below a selected level. To avoid this, industrial users often connect power factor correcting capacitors to the power line along with their inductive loads to compensate and retain the power factor at an economic level.
While there are power factor correcting systems available for large industrial power users, there have been few practical or economical devices for correcting power factors of residential and small business customers. Generally, industrial power factor correcting systems are associated with the equipment for which they are intended to compensate and are activated in coordination with such equipment. In the past, it has not been considered practical or economical for owners of residential property to install power factor correction devices for each possible inductive load. Additionally, inductive devices in residences tend to be activated at random times, for example, under the control of thermostats.
There is a type of integrated circuits or chips referred to as power or energy measurement circuits which have been developed principally for use in solid state power meters for measuring power consumption by electrical utility customers. Such chips measure a number of parameters associated with the flow of AC electrical energy from a source to a customer's electrical installation, including parameters which indicate levels of reactive power or energy drawn by an installation. However, apparatus or methods using such chips to compensate for reactive power drawn for power factor correction purposes are not known to have been previously developed.